Structure of air-water two-phase flow in helically coiled tubes

None

村井 祐一*; 吉川 信治 ; 戸田 信一*; 石川 正明*; 山本 富士夫*

Murai, Yuichi*; Yoshikawa, Shinji; Toda, Shinichi*; Ishikawa, Masaaki*; Yamamoto, Fujio*

ヘリカルコイル伝熱管内の気液二相流挙動を従来より機構的に把握するための取り組みとして、透明なガラス製のヘリカルコイル内の空気と水の混相流を高速度カメラで撮影し、遠心力や管の曲率による二次流れによって直管内の二相流とどのような違いが生じるかを観察した。その結果、液相に作用する遠心力の影響によって直管に比してバブル流の領域が減少すること、曲率の大きな管では圧力変動周波数スペクトルが複数のピークを有すること、重力に対して遠心力が大きな場合には液相が管内のコイル中心から見た外側を主に流れるため、気相の流速が気液合成流速よりも遅くなる場合があることなどが確認された。

Air-water two-phase flow in helicallly coiled tube of 20mm in the internal diameter is investigated ezperimentally to elucidate the effect of centrifugal acceleration on the flow regime map and the local instantaneous flow structure. Three kinds of test tubes including a straight tube are used to compare the flow structure under turbulent flow condition. The superficial velocity up to 6 m/s is tested so that centrifugal Froude number covers a range from 0 to 3. The inter facial structure is visualized from two directions by a high-speed video system with a synchronized measurement of local pressure fluctuation. The results reveral that the flow transition line alters due to centrifugal force acting on liquid phase in the tube. Especially the bubbly fow regime is narrwed significantly. The pressure fluctuation amplitude gets large relatively to the average presure loww as void fraction increases. The Frequency spectra of the pressure fluctuation have plural peaks in the case of strong curvature, implying that the periodicity of slugging two-phase flow is collapsed by internal secondary flow actibated inside liquid phase. Moreover, the substantial velocity of gas phase is slower than the total superficial velocity in case of large Froude number because of biased distribution to the inner surface allowing liquid flow passing outside as like a radial stratified flow.